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Southwest U.S. paleoclimate over the past 30 ky: Insights from speleothem δ18O and growth rate time series

Kevin Meyer

Speleothem calcite stable oxygen isotope compositions (δ18O) commonly reflect the δ18O value of rainfall during the period of formation. Rainfall δ18O changes with climate variations, and thus speleothems can provide terrestrial records of climate variation. Speleothem growth rate serves as a proxy for water availability. This study combines previously published climate records from New Mexico and Arizona speleothems and a Gulf of Mexico (GOM) foraminifera δ18O record with new data from a central Texas speleothem to reconstruct moisture variability in the southwestern US over the last 30 ky, specifically looking at moisture source (Gulf of Mexico vs. Pacific Ocean).

This study suggests moisture dynamics in the southwestern US vary directly with major global climate events. Specifically, the GOM likely shows increased moisture contribution during a warm period known as the Bølling-Allerød (~15-13 ka) with higher water availability in New Mexico and Texas while the following cool period known as the Younger Dryas (~13-11.5 ka) likely has increased Pacific moisture contribution and higher water availability in Arizona.

Growth rates, δ18O values, and U-Th age measurements for speleothems from caves in Texas, New Mexico, and Arizona as well as δ18O and sea surface temperature (SST) values of foraminifera from the Orca Basin in the GOM. The BA warm period is shown in orange and the YD cool period is shown in blue

The Holocene is the warmest period of the record and suggests arid conditions across the southwest. This may indicate that continued anthropogenic warming in the region may lead to increasing aridity.